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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class slo {

    static long[] readLongsLine(int amount) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer tokenizer = new StringTokenizer(reader.readLine());
        long[] result = new long[amount];
        for (int i = 0; i < amount; i++) {
            result[i] = Long.parseLong(tokenizer.nextToken());
        }
        return result;
    }

    private static long treeSize(int n) {
        return (long) (Math.pow(2, n) - 1);
    }

    private static char nextChar(char previousChar, boolean right) {
        if (!right) {
            switch (previousChar) {
                case 'a': return 'b';
                case 'b': return 'a';
                case 'c': return 'a';
            }
        } else {
            switch (previousChar) {
                case 'a': return 'c';
                case 'b': return 'c';
                case 'c': return 'b';
            }
        }
        return 'x';
    }

    private static char[] kWordInternal(char[] buffer, String directions) {
        for (int pos = 1; pos < directions.length(); pos++) {
            buffer[pos] = nextChar(buffer[pos-1], directions.charAt(pos) == '1');
        }
        return buffer;
    }

    static String kWord(int n, long k) {
        char[] result = new char[n];
        long treeSize = treeSize(n);
        if (k <= treeSize) {
            result[0] = 'a';
        } else if (k > treeSize && k <= 2 * treeSize) {
            result[0] = 'b';
            k = k - treeSize;
        } else if (k > 2 * treeSize && k <= 3 * treeSize) {
            result[0] = 'c';
            k = k - 2 * treeSize;
        } else {
            return "NIE";
        }
        return new String(kWordInternal(result, Long.toBinaryString(k)));
    }

    public static void main(String[] args) throws IOException {
        long[] line = readLongsLine(2);
        int n = (int) line[0];
        long k = line[1];
        System.out.println(kWord(n, k));
    }

}